The Japanese consider Miyamoto Musashi to be the best martial artist in their history; although a swordsman, Musashi would have also known Jiu Jitsu.
There are Japanese martial arts. There are individuals that practice them. It would be a stereotype to think that all Japanese practice martial arts. The actual percentage is pretty small and probably is about the same as in the US.
Ustad IP and Bruce Lee
Only Japanese arts were allowed.
Martial Arts refers to the skills used in combat. Every country has martial arts and some originated in Japan, but not all of them.
karateka
You would teach in a martial arts school. The Japanese would call it a dojo.
"Sensei" means 'one who has gone before' and is usually associated with a teacher or mentor. You can call a martial arts instructor 'sensei' in Japanese.
A master
Kendo
They are all martial arts from Asia. Kung fu is from China and karate is from Okinawa. Judo, kendo and aikido are Japanese.
To learn one martial art is impossible. Learning in martial arts does not end.
I think Jet Li is the best at martial arts